Substrate processing and membrane release of transversely-excited film bulk acoustic resonator using a sacrificial tub

A method of forming a filter device using a sacrificial layer and a front side etched cavity comprising:

• forming a recess in a silicon substrate;
• filling the recess with a sacrificial layer;
• forming a bonding oxide (BOX) layer over the substrate and the sacrificial layer filled in the recess;
• bonding a piezoelectric plate to the BOX layer;
• removing the sacrificial layer using an etchant introduced through holes in the piezoelectric plate and BOX layer to form a cavity without removing the BOX layer from over the cavity;
• and
• forming a frontside dielectric over the plate.

A method of forming a filter device using a sacrificial layer and a front side etched cavity comprising:

• forming a recess in a silicon substrate;
• filling the recess with a sacrificial layer;
• forming a bonding oxide (BOX) layer over the substrate and on the sacrificial layer in the recess;
• bonding a piezoelectric plate to the BOX layer;
• forming a conductor pattern on a front surface of the piezoelectric plate, wherein the conductor pattern includes an interdigital transducer (IDT) with interleaved fingers disposed over the recess;
• removing the sacrificial layer using an etchant introduced through holes in the piezoelectric plate and BOX layer to form a cavity where the sacrificial layer was removed without removing the BOX layer from over the cavity;
• and
• forming a frontside dielectric over the plate.